Wave amplifying system



Filed neo. 31 1926 PHIIIIIIFWM tra Panarea May 5, 1931 ETE STATES Laica?.

oraria EDMOND BRUCE AND HARALD' T. FE11S, OF RED BANK, NEW JERSEY, ASSIGNO'RS TO BELL TELEPHONE LABGRATORIES, INCGRPORATED, OF NEN YORK, N. Y., A CORPORA- TION OF NEW YORK VAVE AMLXFYING SYSTEM Application filed December 31, 1926'.

'A inductance of its tuned circuit, a coil inserted between the antenna and ground to reduce the apparent antenna resistance. The middle of the coil is connected to the amplifier filaments,

the grounded end of the coil is connected to the grid of one of the amplifier tubes and to the plate of the other, and the other end of the coillis connected to the other grid and to the other plate of the amplifier. The coil is also included in the grid-filament circuit oi` the first detector, to deliver signaling waves to the detector. The coil comprises three strands insulated from each other for direct current, but forming' a single inductance for high frequency. rlhe strands afford D. @.paths, of

'1" proper impedance to high frequency, for supplying the amplifier filaments with heating current from a grounded filament battery, for inductively connecting the grid of each tube ci the amplifier to the filament of the tube,

'i 'and for supplying space current to the tubes of the amplifier. i

The amplifier in the antenna circuit is made to produce large amplification of the signaling voltage. it has been found that,where the total amplification of the system is ver) great, the ratio of the volume of the signal received at the output of the system to the volume of the received tube noise is increased by increasing tbe proportion of the total amplification which is obtained at the frequency ot the short waves received by the antenna.

The single figure of the drawing shows this successive detection short wave radio receiving system.

In the figure a variable coupling condenser 2connects an antenna 1 to `round through a circuit comprising an inductance coil 3 shunted by a condenser t.

A push-pull circuit of the type disclosed in U. S. Patent No. 1,472,470, October 30,

Serial No. 158,170.

1923, to Hartley, but adjusted to a non-oscillatory condition, is employed asa regenerative amplifier A. This circuit includes electric space discharge tubes 5 and 6 connected in push-pull relation by artuned circuit comprising the coil 3 and the condenser 4.

The coil 3 comprises a coil or helix of cop? per tubing 10, enclosingan insulated wire 11 and an insulated wire 12, and forming a conductor of very low resistance for high frequency waves. Atthe upper end of the coil 3 the coils 10,11 and 12 are interconnected by, condensers 15, each of which is of low or negligible reactance at the Wave lengths to be received, which may be, for example, of the order of 25 meters. The three strands 10,-11 and 12 of coil 3 are closely coupled electromagnetically. For alternating current they7 constitute one coil or winding. For high frequency the resistance and the inductance of the coil 3 are substantially the resistance and the inductance of coil 10, and the resistance and the inductance of each half of coil 3 are substantially the resistance and the inductance of half of coil 10.

The upper and lower ends of strand 10 are conductively connected through conductors 21 and 22, respectively, to the grids of tubes 6 and 5, respectively, and the midpoint o'l" this strand is conductively connected to one each of thelilaments of these tubes. The other side of each of these filaments is conductively connected to the midpoint of the strand 11, and the lower ends of strands 10 and 11 are conductively connected across a grounded battery 23, which supplies heating current to the filaments through the lower halves of strands 10 and 11.

The conductor 21 and the upper half of strand 1() form a conductive path for fixing the average potential of the grid of tube 6 with reference to its filament, and the conductor 22 and the lower half of strand 10 forni a conductive path for fixing the average potential of the grid of tube 5 with reference to its filament.

The upper half of coil 3 delivers the alternating current input voltage for tube 6 across the grid and the filament of that tube, and the lower half of coil 3 delivers the alternating Cai current input voltage for tube 5 across the grid and the filament ot that tube.

The upper and lower ends oi strand l2 are conductively connected, through conductors and Q4, respectively, to the plates of tubes 5 and 6, respectively, and the lower ends ot strands ll and 12 are conductively connected across a source of unidirectional electrometive force., comprising a battery and a variable resistance 3l in series. From this source, space current is supplied to tube 5 through a circuit extending 'from the resistance 3l through strand l2 and conductor 25, through the space discharge path from the plate to the filament of the tube, and through the lower half oi strand 1l, to battery 30'. Space current is supplied to tube 6 through a path extending from resistance 3l, through conductor 24C, through the space discharge path troni the plate to Vthe lilament of the tube, and through the lower halt ot strand 11, to battery 30.

The output electron'iotive 'torce across the plate and the filament ot tube 6 is delivered to the lower halt of coil 3 and the output electromotive torce across the plate and the lilainent of tube 5 is delivered to the upper hali" ot coil 3.

Tie output electrodes of each of the tubes 5 and (S are coupled to the input electrodes ot' the tube by a resonant circuit comprising the iiuliu-taiu'e 3 shunted b v two capacity branches, one consisting `oi" thc condenser -l and one comprising the coupling` condenser in series with the .impedance ot' the path troni the antenna to earth through the natural caparity oif 'the antenna to ground.

The degree ot regeneration or ainplilicati i in the ainplilier, 'for a given setting oi: the coupling condenser 2, can be controlled by varying resistance 3l. to alter the cliective plate voltage of the, amplifier. jin approxiinatc a ljustnient ol the amount oit regeneration can be obtained by means ot rcs' "tance il with coinlenser 2 adjusted at a desired capacity and line adjiestnientcan l' nude by li rezulliustnicnt oiicondenser. iwever, it sireal. the resistance ill can be omitted and the amount ot regeneration be controlled by varying condenser 2, varying condenser l approximately simultaneous-:ly to niaintain the receiver tuned to the frequency ot the waves to be received.

The conductor 2l, leading from the u per cnd et coil 3, and a conductor 35. Ace d ng ,from the lower end ol? the coil, connect the coil in the grid-filament circuit ot a iirst detector il() which with its cooperating eating oscillator -i-'l steps down the frequency of the signal waves delivered by'coil 3 and transmits the signal waves ot reduced frequency te an interi'nediate frequency amplifier 50, ifft'ter amplitication in amplifier the signals which may be speech signals, for example, are detected b v a low frequency detector (il),

which delivers them to a telephone receiver To. or other signal indicating` means.

'l`he push-pull amplifier ot the type described is capable otl vigorous regenerative ac,- tion and eliects high anulilitication for short waves or waves ot very high radio frequencies.

The lou' halves ot the strands 10 and 1l are included in the amplifier resonant circuit, which is tuned to the signaling frequencies. The amplifier filaments are grounded vtor direct current but are maintained at a potential which :is higher than ground potential by an amount equal to halt ot the voltage drop across coil B ior high frequencies. Therefore, the whole et the voltage across the coil 3 can be applied across leads 21 and 35 to the input circuit o" detector l0 and yet the cus'stomar,f desirable groundingv ot the detector lilai'nent i'or the signaling frequency can be ellected, even in cases in which the lead 35 is conductively connected to the ilainent ot the detector.

llloreover,

with the filaments thus at a high :nnplilier is symmetrically connected to tue path including the coupling condenser Q and the natural capacity ot the antenna to Grounding ot the filaments oit tu es 5 and G 'tor direct current, while they are maintained it the required potential above ground tor iigh trequcncies, avoids any necessity tor in- ;ulating their heating current supply source c space current sup'ily source from earth or high trequencies. The direct current external space current paths tor the tubes 5 and o cannot have an unduly great shunting e'tect non the alternating current external platefleunent paths for the tubes, since those direct current paths include, refn'iectively, the induciances et these alternating current paths.

rl`ube noise is the limiting 'factor in the amplification that may be usefully en'iployed in a radio receiver, as tor example, in receiving speech signals or signals transmitted tor use in measuring radio lield strengths or wave intensities. In receiving sets in which the available amplilication is such that an ppreciable output indication or deflection results troni the inherent tube noise, additional anipliication can be oi" no benefit. As regards sensitivity, such a receiver or measuring set can well be rated by its lield strength equivalent ot' the tube noise output indication or de'l'lection.

Increasing't-he ratio ot gain to tube noise in the amplifying system will increase `the sei'isitivity of such a receiver, and the sensitivity'can be materially increased by employing a strongly regenerative amplilier giving a large amplification of short waves in the antenna, and thus reducing the requisite intermediate frequency amplification, or, in other Words, thus substituting regenerative amplification at the incoming frequency for a. material portion of the intermediate-frequency amplification; for experiment has shown that the amplification, for a given amount of tube noise, increases as the resonant frequency is increased.

At 25 meters the increase obtained in ainplification for the same tube noise was about six times When a large amount of regenerative amplification of the short Waves Was substituted for a material portion of the intermediate frequency amplification by introducing the amplifier A in the antenna. The voltage amplication of the .short Waves in the antennaq produced by the regenerative amplifier. is preferably of the order of at least 10 times, the function of the short Wave amplifier being more than merely to increase the frequency selectivity of the system. rlhe amplification produced in the intermediate frequency amplifier may be the largest amplification, at the intermediate frequency, for which the tube noise can be tolerated.

The term short Waves is herein employed to' designate Waves not longer than abouty 21a meters.

A ground or earth connection may be a connection to any mass to Which the connection serves the same purpose as Wouldy a connection to earth or to any capacity of extremely great magnitude.4

lli/That is claimed is:

l. An amplifier comprising a plurality of electric space discharge devices connected in balanced relation to operate Without frequency translation, each of said devices having a cathode, an anode and a grid, a cornmon input circuit and a common output circuit for said devices, said common input circuit being connected to ground, means for impressing signal variations upon said common input` circuit, and means for connecting said cathodes to a point on said input circuit electrically remote from said ground connection.

Q. An amplifier comprisingr a. plurality of electric space discharge devices connected in balanced relation. to operate withoutfrequency translation, each of said devices having a cathode, an anode and a grid, a common input circuit and a. common output circuit for said devices, said common input circuitbeing connected to ground., coupling means whereby signal variations produced in said output circuit are impressed upon said coinmon input circuit, means for impressiiio1 signal variations on said common input circuit, and Yineans for connecting'said cathodes to a point on said input circuit electrically remote from said ground connection.

3. An electric space discharge tube having an anode and a thermionic cathode, a high frequency alternating current Work circuit connected across said anode and said cathode, said Work circuit including a plurality of conductors insulatedl from each other edectively for direct current, a source of heating current connected to said cathode through at least one of said conductors, and a source of space current connected to said anode through another of said conductors, said other conductor being distinct from said first mentioned conductors in said alternating current Work circuit.

l. Amplifier means comprising tWo` electric space discharge tubes, each having an anode, a therinionic cathode and an impedance control element, an iiiductance element for connecting said tubes in push-pull relation, said inductance Velement including a plurality of conductors insulated from each other effectively forA direct currents, rand sources of heating current and space current connected to said cathode and anode respectively through didereiit conductors in said inductance. c

5. An electric space discharge tube having an anode and a thermionic cathode, a high frequency alternating current Work circuit connected acros said anode and said cathode, said Work circuit including a plurality ofconductors insulated from each other effectively for direct currents, a source ofheating current connected to said cathode through atleast one of said conductors, a

source of space current connected tok saidr` anode through another of said conductors,

said other conductor being distinct from said first mentioned conductors in said alternating current Worky circuit, meansfor maintaining said cathode at an alternating potential materially different from ground, and meansgrounding said sources andsaid anode for high frequency.

6. An electric space discharge tube having an anode and a thermionic cathode, al high.

means for maintaining said sources at sub-.

stantially the saine high frequency potential as said anode. n

7 An electric space discharge tube having an anode, a thermionic cathode and an impedance control element for controlling the impedance of the space discharge path between said cathode and said anode, an alterliti nating current input circuit connecting said,

cathode and said control element of said tube, theA input circuit including a plurality ofconductors insulated from each other eectively for direct currents, means for supplying short Waves to said input circuit, a source of heating current connected to vsaid cathode through at least one of said conductors, a source of space current connected to said anode through another of said conductors, said other Conductor being' distinct from said first mentioned conductors in said alternating current Work circuit, means for maintaining said cathode at an alternating potential materially dierent from ground, and means grounding said sources and said control element for high frequency.

8; In combination with an antenna, a short Wave regenerative amplilier comprising two electric space discharge tubes, each having an anode, a cathode, and an impedancek control element, a tuned circuit comprising inductance and capacity and connecting said tubes in push-pull relation with the cathodes connected to the midpoint on said inductance and With one end of said inductance connected to said antenna and to the anode of one tube and to the control element of the other tube, and with the other end of said inductance connected to ground and to the other plate and control element of the amplifier, a grounded source of cathode heating current, and a source ot unidirec, tional space current for said tubes, said inductance comprising conductors insulated from each other for connecting said lirst source to said cathodes, for connecting the impedance control element of each tube of the amplifier to its cathode, and for connecting said second source to the anode of each tube.

In Witness whereof, We hereunto subscribe our names this23d day of December, A. D.

EDMOND BRUCE. HARALD T. FRIIS. 

